When a Lambda outgrows itself

How a function grows to thousands of lines, and what that costs.

A streaming variant of the ETL landed as one commit with a processor Lambda of several thousand lines. It worked, and it was the moment the Java rewrite five months later became inevitable.

A Lambda that size has no tests you can run locally, a cold start you can feel, and a fifteen-minute ceiling it is always near.

Takeaway

The size was not the problem. The size was the symptom of a workload that wanted a long-running process with a real heap.

Client engagement, 2021 to 2026. Names, identifiers and internals are generalised.